1. Field of the Invention
The present invention relates to a diagnostic device for diagnosing a state of a lamp and a lamp ballast circuit by using the diagnostic device.
2. Description of the Related Art
A conventional diagnostic device for diagnosing a state of a lamp is separately formed from that of a lamp driving circuit. In addition, the conventional diagnostic device may not diagnose the lamp at an end of lamp life (EOLL) condition. Further, since respective diagnostic devices may be designed and manufactured according to types of electronic stabilizing devices of the lamp, manufacturing cost may be increased, and additional processes may be performed.
At the end of lamp life (EOLL) condition, when a lamp is compared with a normal lamp, the lamp voltage and current vary asymmetrically and also the filament equivalent resistance increases. When a ballast device is driven in this state, the ballast device supplies a predetermined amount of current to the lamp, and a power loss increases, caused by the filament equivalent resistance increase at the end of lamp life (EOLL) condition. In addition, heat can be generated in a filament according to the increase of resistance, thus raising the temperature of the filament. Further, as time passes in the end of lamp life (EOLL) condition, the temperature of the filament may continuously increase, and therefore plastic elements contacting the filament in the lamp may melt by the increased temperature. In this case, since constituent elements connecting a lamp to another lamp may be loosened, the lamp may be separated from the other lamp.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.